Twenty-five years ago we began to investigate an outbreak of rachitic bone disease in adolescent, female New World primates residing at the Los Angles Zoo. Our investigation of this "experiment of nature" and that of an adolescent human female with a similar phenotype led us to the discovery of a novel means for vitamin D and estrogen resistance in primates, including man. We coined these resistance-causing proteins the vitamin D response element binding protein (VDRE-BP) and estrogen response element binding (ERE-BP) for their ability to compete in trans with the liganded vitamin D receptor (VDR) and estrogen receptor 1 (ER1) for their cognate response elements, identifying them as nucleic acid binding proteins in the heterogeneous nuclear ribonucleoprotein C (hnRNPC) family. Recent work has led us to realize that the ability of these hnRNPs to alter steroid hormone-directed gene expression is not limited to their dominant-negative actions at the level of transcription. By virtue of their capacity to interact with single-strand DNA (ssDNA), ssRNA as well as double- strand DNA (dsDNA), these hnRNPs have the potential to exert control over gene expression at multiple sites in the cell. Here we theorize that a specific hnRNP can act as a multi-site participant in the synchronized expression of a single gene product by way of regulating, in succession, chromatin remodeling (ssDNA binding), transcription (dsDNA binding), splicing (ssDNA and ssRNA binding) and microRNA (miRNA;ssRNA binding). Because both the human and subhuman primate experiments of nature in hnRNP overexpression we have studied resulted in coincident vitamin D- and estrogen-antagonism on the growing skeleton of adolescent females, here we will concentrate on growing bone and the osteoblast as natural targets for these hnRNPs.
Three specific aims are proposed: 1) using chromatin modification/precipitation, over/under expression and novel cell free translation technologies, explore the impact of hnRNPs on the cells responsible for 1,25- dihydroxyvitamin D and estradiol-driven bone growth;2) employ new RNA immunoprecipitation and micro- RNA methodology to study the versatility of these hnRNPS to control transcript splicing and handling by directed binding to RNA products of the same gene whose expression is simultaneously regulated at the level of chromatin remodeling and transcription;and 3) ascertain the composite effect of these hnRNPs on the growing, adolescent skeleton by targeted transgenic overexpression of the VDRE-BP and ERE-BP hnRNPs in mouse bone. It is our expectation that the proposed research will pave the way to a mechanistic understanding of how these multi-functional hnRNPs control the process of sterol/steroid hormone-regulated gene expression in growing bone and delineate novel points of potential therapeutic intervention in that process.
Vitamin D and estrogen are two steroid hormones long recognized for their ability to influence the growing skeleton. Twenty five years ago we began to investigate an outbreak of rickets in adolescent, female New World primates residing at the Los Angeles Zoo, identifying proteins in the heterogeneous nuclear ribonucleoprotein C (hnRNPC) family, the vitamin D response element binding protein (VDRE-BP) and estrogen response element binding (ERE-BP) which caused resistance to the actions vitamin D and estrogen hormones on the skeleton. By virtue of their capacity to interact with single-strand DNA (ssDNA), ssRNA as well as double- strand DNA (dsDNA), we have planned experiments to test our theory that the VDRE-BP and ERE-BP can act in bone as a multi-site participant in the synchronized expression of a single gene product by way of regulating, in succession, i) chromatin remodeling, ii) transcription, iii) transcript splicing and iv) transcript handling.
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